Fig. 5.

Multiple diffraction orders are observed in photonic balls from larger colloids. (A–D) SEM micrograph (A) and optical properties (B and C) of photonic balls prepared from 610-nm colloids. Two diffraction orders are visible as polychromatic spots in the optical micrographs in top (B) and side (C) illumination. The positions of the colors on the ball coincide with theoretical expectations based on a 1D model of grating diffraction on a curved surface (D). (E–H) SEM micrograph (E) and optical properties (F and G) of photonic balls prepared from 1,060-nm colloids. The optical micrographs in top (F) and side (G) illumination show three diffraction orders, the position of which coincides with theoretical expectations (H). The color patches assigned to the individual diffraction orders in the model are slightly offset for better visibility. (All scale bars, 10 µm.) (I and J) SEM and optical micrographs of a close-packed monolayer of 610-nm colloids deposited onto a 50-µm bead, mimicking the periodic arrangement of the colloids at the surface of a photonic ball. The monolayer-on-microbead architecture shows similar coloration, implying that grating diffraction is the origin of the color.